Recent climate change has advanced seasonal timing (phenology) in many animals and plants, particularly in temperate and higher latitude regions. The population and fitness consequences of these phenological shifts for insects and other ectotherms have been heterogeneous: warming can increase development rates and the number of generations per year (increasing fitness), but can also lead to seasonal mismatches between animals and their resources and increase exposure to environmental variability (decreasing fitness). The developmental responses of insect populations to temperature contribute to seasonal adaptation to local climate conditions; but climate change can potentially disrupt seasonal timing of juvenile and adult stages and consequently population fitness. We investigate these issues using a global dataset for the developmental responses of insects to temperature, focusing on two types of traits: lower temperature thresholds for development (T0), and the cumulative degree-days required to complete development (DDD). We explore how these traits vary across gradients in seasonality (latitude). We then use the traits to predict developmental timing and temperatures experienced during development for multiple generations within seasons and across years. Our preliminary analyses suggest that the curvature describing variation in temperatures and generation length peaks at mid latitudes where the growing season is sufficiently long to experience pronounced seasonality. Phenological advancements over recent decades peak at poleward latitudes, whereas increases in the potential number of generations peak at mid latitudes. Shifts in developmental and adult temperatures vary. Developmental shifts due to climate change will have complex implications for selection and fitness in seasonal environments.